This proposal represents a continuation of our studies which were initiated over 12 years ago and since have stimulated extensive efforts to understand the phenomenon of ischemia/reperfusion injury in the mammalian heart. The studies are designed to examine the participation of the polymorphonuclear leukocyte (PMN), oxygen radicals, and components of the complement system (rabbit heart) along with the synthesis of stress proteins as factors which determine the extent of myocardial injury. Studies will be conducted in the anesthetized dog subjected to temporary left circumflex coronary artery occlusion followed by reperfusion (6 hours to 4 days). We will employ a modified version of the classical animal model of regional ischemia in which retrograde flow from the occluded coronary bed is permitted to occur thereby intensifying the severity of ischemia in the risk region and thus reducing the variability in infarct size noted by many who employ the canine heart. The role of the neutrophil adhesion promoting glycoprotein receptor, CD11b/CD18, a participant in various effector functions and cellular collaboration in the inflammatory response will be explored with the use of selected monoclonal antibodies unknown to bind homologous integrins. The rapid synthesis of "stress proteins" in response to myocardial ischemia and its ability to protect the jeopardized heart will be a focus of this investigation. An effort to determine the time course for the appearance and disappearance of the 71 kD protein will be undertaken. The quantitative determination of the 71 kD protein will be employed in these studies. The effects of selected pharmacologic interventions will be assessed in terms of infarct size, neutrophil infiltration of ischemic myocardium, functional integrity of ischemic microvasculature, regional myocardial blood flow (micropshere method), and ventricular function. Infarct size and the anatomic area at risk will be determined by a dual staining technique and confirmed by histology. Permeability changes in the microvasculature will be assessed with the use of intramyocardial ultrasonic crystals. The long range goals of these studies are to determine if modification of leukocyte function, complement activation or the endogenous synthesis of stress proteins in response to regional ischemia can reduce the degree of irreversible myocardial injury associated with regional ischemia and/or reperfusion. The outcome of these investigations could lead to a better understanding of the dynamics of PMN interaction with target tissues and pharmacologic interventions to protect the heart that undergoes reperfusion as in the case of thrombolytic therapy, angioplasty or after termination of global-ischemic arrest during cardiopulmonary bypass. The proposed studies are designed to bridge the gap between in vitro experiments and experimentally based in vivo models of myocardial ischemia/reperfusion.